Estimation procedures and error analysis for inferring the total plutonium (Pu) produced by a graphite-moderated reactor

Graphite isotope ratio method (GIRM) is a technique that uses measurements and computer models to estimate total plutonium (Pu) production in a graphite-moderated reactor. First, isotopic ratios of trace elements in extracted graphite samples from the target reactor are measured. Then, computer models of the reactor relate those ratios to Pu production. Because Pu is controlled under non-proliferation agreements, an estimate of total Pu production is often required, and a declaration of total Pu might need to be verified through GIRM. In some cases, reactor information (such as core dimensions, coolant details, and operating history) are so well documented that computer models can predict total Pu production without the need for measurements. However, in most cases, reactor information is imperfectly known, so a measurement and model-based method such as GIRM is essential. Here, we focus on GIRM's estimation procedure and its associated uncertainty. We illustrate a simulation strategy for a specific reactor that estimates GIRM's uncertainty and determines which inputs contribute most to GIRM's uncertainty, including inputs to the computer models. These models include a “local” code that relates isotopic ratios to the local Pu production, and a “global” code that predicts the Pu production shape over the entire reactor. This predicted shape is included with other 3D basis functions to provide a “hybrid basis set” that is used to fit the local Pu production estimates. The fitted shape can then be integrated over the entire reactor to estimate total Pu production. This GIRM evaluation provides a good example of several techniques of uncertainty analysis and introduces new reasons to fit a function using basis functions in the evaluation of the impact of uncertainty in the true 3D shape.     

Evaluation of the mean ice ratio as a function of temperature in a heterogeneous food: Application to the determination of the target temperature at the end of freezing

The freezing process is widely used in the food industry. In the 70s, French regulation authorities have created in collaboration with the food industry the concept of «surgélation» process with the objective of improving the image of high quality frozen foods. The process of “surgélation” which could be translated as “super freezing” corresponds to a freezing process for which a final temperature of −18 °C must be reached “as fast as possible”. This concept was proposed in opposition to a conventionally “freezing” process for which no specific freezing rate is expected and the final storage temperature can be of −12 °C only. The objective of this work is to propose a methodology to evaluate the mean amount of frozen ice in a complex food as a function of temperature and to deduce a target temperature that must be considered as the temperature for which the food may be considered as “frozen”. Based on the definition proposed by the IIF-IIR red book, this target temperature has been defined as the temperature for which 80% of the freezable water is frozen. A case study is proposed with a model food made of two constituents.     

Is stochastic equivalent linearization a subtly flawed procedure?

The standard equivalent linearization procedure for estimating the mean and variance of the response of nonlinear dynamic systems has proved to be an unusually effective technique. For over forty years there has been general agreement about the procedure to be followed. Recently two independent claims have been made that the standard procedure harbors a subtle flaw. In place of the standard procedure, essentially the same alternative procedure was claimed to be the “correct” procedure, even though, in the test cases investigated, the alternative “correct” procedure produced estimates with greater errors than the “incorrect” standard procedure. The present note investigates the claim that the standard procedure is flawed and finds that: (a) there is no subtle flaw in the standard procedure; (b) the proposed alternative procedure differs from the standard procedure in that it employs a different criterion for selecting the optimum linear approximation; (c) there is also no flaw in the proposed alternative procedure; but, (d) there does not seem to be any practical advantage to using the proposed alternative, since the standard procedure is simpler and more accurate.     

A preliminary evaluation of the impact of local accident information on the public perception of road safety

The World Health Organisation (WHO) estimate that road traffic accidents represent the third leading cause of “death and disease” worldwide. A number of countries have, therefore, launched safety campaigns that have reduced their fatalities. In almost every case, however, this reduction has not been matched by a fall in the total frequency of road traffic accidents. Low-severity incidents remain a significant problem. “Attribution error” provides one plausible explanation for this phenomenon. Most drivers believe that they are less likely to be involved in an accident than other motorists. Existing road safety campaigns do little to address this problem; they focus on national and regional statistics that often seem remote from the local experiences of road users. This paper, therefore, describes the design and development of a system to provide the general public with access to information on the location and circumstances of road accidents in a Scottish city. The closing sections describe the initial results from a psychometric study that is intended to determine whether the information provided by such an application will have any impact on individual risk perception.     

The effect of micro-alloying addition of Cr on age hardening of an Mg–Zn alloy

This work reports a chemical method called “co-deposition route” for fabricating ND (nanodiamond)/Cu composite at a molecular-level mixing. The main procedure of “co-deposition route” includes four steps. ND particles have been functionalized by HF acid before co-deposition. SEM, HRTEM (high-resolution transmission electron spectroscopy), XRD (X-ray diffraction), EDS (energy-dispersive spectrum analysis) and optical microscope were carried out to characterize the as-prepared composite powders and bulk composites. Results indicated that copper matrix composite with a homogeneous dispersion of functionalized ND particles can be prepared. The modification of ND particles was performed by HF (30 vol%) acid at 70 °C, and CF bond was successfully detected by XPS (X-ray photoelectron spectrum) and IR (Infrared spectroscopy). The properties of relative density, microhardness and electric conductivity of ND/Cu composites have been measured. With the comparison of conventional methods, it showed that the as-prepared ND/Cu composites with good combined performances have a promising future for industry application.     

A new estimator for sensitivity analysis of model output: An application to the e-business readiness composite indicator

In this paper we propose and test a generalisation of the method originally proposed by Sobol’, and recently extended by Saltelli, to estimate the first-order and total effect sensitivity indices. Exploiting the symmetries and the dualities of the formulas, we obtain additional estimates of first-order and total indices at no extra computational cost. We test the technique on a case study involving the construction of a composite indicator of e-business readiness, which is part of the initiative “e-Readiness of European enterprises” of the European Commission “e-Europe 2005” action plan. The method is used to assess the contribution of uncertainties in (a) the weights of the component indicators and (b) the imputation of missing data on the composite indicator values for several European countries.     

Mitigating the effects of system resolution on computer simulation of Portland cement hydration

CEMHYD3D is an advanced, three-dimensional computer model for simulating the hydration processes of cement, in which the microstructure of the hydrating cement paste is represented by digitized particles in a cubic domain. However, the system resolution (which is determined by the voxel size) has a prominent influence on the simulation results and, thus, is difficult to choose a priori. In this paper, it is shown that the effects of system resolution on the simulation results are mainly due to the lack of considerations of the diffusion-controlled reactions in the model. A new concept “hydration layer” is proposed for mitigating the effects of system resolution on the model predictions. By performing simulations with different system resolutions, the robustness of the improved model is demonstrated. Comparisons of model predictions with experimental measurements further demonstrate that the use of hydration layer can successfully mitigate the bias brought by the system resolution.     

Comparison of pure and “Latinized” centroidal Voronoi tessellation against various other statistical sampling methods

A recently developed centroidal Voronoi tessellation (CVT) sampling method is investigated here to assess its suitability for use in statistical sampling applications. CVT efficiently generates a highly uniform distribution of sample points over arbitrarily shaped M-dimensional parameter spaces. On several 2-D test problems CVT has recently been found to provide exceedingly effective and efficient point distributions for response surface generation. Additionally, for statistical function integration and estimation of response statistics associated with uniformly distributed random-variable inputs (uncorrelated), CVT has been found in initial investigations to provide superior points sets when compared against latin-hypercube and simple-random Monte Carlo methods and Halton and Hammersley quasi-random sequence methods. In this paper, the performance of all these sampling methods and a new variant (“Latinized” CVT) are further compared for non-uniform input distributions. Specifically, given uncorrelated normal inputs in a 2-D test problem, statistical sampling efficiencies are compared for resolving various statistics of response: mean, variance, and exceedence probabilities.     

Study of the compatibility between criteria in a set of materials requirements: Application to a machine tool frame

This contribution to materials selection theory aims at developing methodological methods and tools to analyse a complex set of material requirements with the objective of forecast whether there are materials that can fulfil it, or alternatively, if multi-materials selection is more likely to provide a solution. This “pre-analysis” of requirements examines the two main reasons which may prevent a single material solution: nonuniformity of materials space filling, or intrinsic contradiction between properties.A variety of statistical tools is used, based on Multivariate Analysis Methods as Principal Component Analysis (PCA) and the estimation of density distribution in the materials space. These tools allow to evaluate the “statistical compatibility” between the requirements and the available materials, and provides an estimate of the likelihood to find a single material solution or not. The methodology is applied to the research of a material for a machine tool frame.     

An Investigation of the Measurements Systems Analysis “Analytic Method” for Attribute Gages

Three automotive corporations have developed and sanctioned the recently revised reference manual entitled Measurement Systems Analysis. This “standard” contains a procedure, called the “analytic method,” whose purpose is to estimate the gage bias and gage repeatability of an attribute gage. An improved estimation procedure for this standard is presented. The improved estimation procedure yields more accurate estimates than those obtained using the procedures currently presented in the standard. In addition, the improved procedure allows more flexibility in data collection than the current test protocol. A simulation study that evaluates the estimation procedure of the current standard and compares it with the improved estimation procedure is presented. Errors that are contained in the present standard are also noted.     

A third-order bias corrected estimate in generalized linear models

Cordeiro and McCullagh (J Roy Stat Soc Ser B 53:629–643, 1991) derived a second-order bias-corrected estimate, which displays smaller bias than the classical maximum likelihood estimate in generalized linear models. This estimate, although consistent, can display pronounced bias in small to moderately large samples, as shown by Monte Carlo simulations here. In this paper, we obtain a simple matrix formula for the bias of order n ^-2 of this estimate, where n is the sample size, and define a third-order bias-corrected estimate in this class of models, which displays much smaller bias in small samples. In particular, some Monte Carlo simulations show that our new estimate can deliver substantial improvements in terms of bias and mean squared errors over the usual maximum likelihood estimate and Cordeiro and McCullagh’s estimate.     

The impact of work input to sorption cyclesImpact de l'apport en énergie sur les cycles à sorption

In recent years the interest in cooling machines or heat pumps combining the principles of compression and sorption technology is increasing. The reason is that both technologies have specific drawbacks which can be overcome by the combination. Our discussion is centred around absorption cycles which use a compressor, and, consequently, an input of a significant amount of mechanical work in addition to heat. In most publications cycles of this kind are discussed in terms of one single COP as usual in the refrigeration industry. This, however, is wrong from a thermodynamic, and misleading from a technical and economical point of view. In order to highlight the need for a strict thermodynamic approach, a fundamental difference between distinct kinds of work input, namely “recoverable work”, “dissipative work” and “heat transformation work” is discussed in the first part of the paper. In the second part it is shown how the input of both work and heat into a energy conversion system has to be handled with both mechanical and thermal COP. The method is thermodynamically sound and straightforward, technically feasible and easy to apply, and most quickly transferred into economical terms. In the third part, a practical example of a compression–absorption hybrid is investigated.     

A design-centered approach in developing Al-Si-based light-weight alloys with enhanced fatigue life and strength

Material heterogeneities and discontinuities such as porosity, second phase particles, and other defects at meso/micro/nano scales, determine fatigue life, strength, and fracture behavior of aluminum castings. In order to achieve better performance of these alloys, a design-centered computer-aided renovative approach is proposed. Here, the term “design-centered” is used to distinguish the new approach from the traditional trial-and-error design approach by formulating a clear objective, offering a scientific foundation, and developing a computer-aided effective tool for the alloy development. A criterion for tailoring “child” microstructure, obtained by “parent” microstructure through statistical correlation, is proposed for the fatigue design at the initial stage. A dislocations pileup model has been developed. This dislocation model, combined with an optimization analysis, provides an analytical-based solution on a small scale for silicon particles and dendrite cells to enhance both fatigue performance and strength for pore-controlled castings. It can also be used to further tailor microstructures. In addition, a conceptual damage sensitivity map for fatigue life design is proposed. In this map there are critical pore sizes, above which fatigue life is controlled by pores; otherwise it is controlled by other mechanisms such as silicon particles and dendrite cells. In the latter case, the proposed criteria and the dislocation model are the foundations of a guideline in the design-centered approach to maximize both the fatigue life and strength of Al-Si-based light-weight alloy.     

Local and global heat transfer coefficients of a stabilised ice slurry in laminar and transitional flows

The thermal behaviour of a new two-phase secondary refrigerant has been analysed. The “stabilised ice slurry” is a suspension in a low viscosity oil of ultraporous polymeric particles filled with water. In order to determine the convective heat transfer coefficient of this secondary refrigerant with water–ice phase change, an experimental set-up was built. It allows determining the local heat transfer coefficients inside two heat exchangers, having rectangular sections (80 × 8 mm²) of 1 m length, by mean of fluxmeters located along the working section. The slurry is first cooled and frozen in one of the exchangers, then heated and melted in the other exchanger. The results obtained for laminar or transitional flows shows that the heat transfer coefficients of the ice slurry are obviously higher than the heat transfer coefficients obtained with the single-phase fluid (oil). Correlations giving the local and global Nusselt numbers, depending on the Graetz or Reynolds numbers and on the particle mass fraction, have been established.     

Estimation of failure intensity for the Weibull process

A Weibull process/non-homogeneous Poisson process is commonly used to analyze the failure behavior of repairable systems. The object of the present study is to obtain exact estimates of the failure intensity of this model at the time of n failures. The resulting MLE estimate is biased and the corrected version for biasedness along with some approximate estimates is given. An analytical and numerical comparison of the relative efficiencies of the MLE of the exact biased, approximated biased, exact unbiased and approximated unbiased of the intensity function is presented. It will be shown that for small n (n < 30) there is quite a large relative difference between the mean squared errors of the exact and approximate estimates of the intensity function. Real failure data are used to illustrate the difference between the exact and approximate estimates of the intensity function.     

Corrosion resistance of AlN–SiC–TiB2 composite in air

The oxidation kinetics of AlN–SiC–TiB₂ composite in air has been investigated in terms of a theoretical analysis associated with the experiment data. The effects of temperature and temperature heating rate on the oxidation reaction have been discussed by using the “characteristic oxidation time”. The results show that the calculated results by our model can give a good agreement with the experimental data. From this study it is shown that, the “characteristic oxidation time” is a very useful parameter for comparing the property of oxidation resistance for different composites.     

Analysis of OREDA data for maintenance optimisation

This paper provides estimates for the average rate of occurrence of failures, ROCOF (“failure rate”), for critical failures when also degraded failures are present. The estimation approach is exemplified with a data set from the offshore equipment reliability database “OREDA”. The suggested modelling provides a means of predicting how maintenance tasks will affect the rate of critical failures.     

Costlets: A Generalized Approach to Cost Functions for Automated Optimization of IMRT Treatment Plans

We present the creation and use of a generalized cost function methodology based on costlets for automated optimization for conformal and intensity modulated radiotherapy treatment plans. In our approach, cost functions are created by combining clinically relevant “costlets”. Each costlet is created by the user, using an “evaluator” of the plan or dose distribution which is incorporated into a function or “modifier” to create an individual costlet. Dose statistics, dose-volume points, biological model results, non-dosimetric parameters, and any other information can be converted into a costlet. A wide variety of different types of costlets can be used concurrently. Individual costlet changes affect not only the results for that structure, but also all the other structures in the plan (e.g., a change in a normal tissue costlet can have large effects on target volume results as well as the normal tissue). Effective cost functions can be created from combinations of dose-based costlets, dose-volume costlets, biological model costlets, and other parameters. Generalized cost functions based on costlets have been demonstrated, and show potential for allowing input of numerous clinical issues into the optimization process, thereby helping to achieve clinically useful optimized plans. In this paper, we describe and illustrate the use of the costlets in an automated planning system developed and used clinically at the University of Michigan Medical Center. We place particular emphasis on the flexibility of the system, and its ability to discover a variety of plans making various trade-offs between clinical goals of the treatment that may be difficult to meet simultaneously.     

Investigation of High-Velocity Suspension Flame Sprayed (HVSFS) glass coatings

High-Velocity Suspension Flame Spraying (HVSFS) has recently emerged as a potential alternative to conventional HVOF-spraying: employing liquid suspensions instead of dry powder feedstock enables the use of very fine grain-sized particles, resulting in small-sized lamellae. Thin, low-porosity coatings can thus be manufactured. This paper details the first attempt at manufacturing glass coatings using the HVSFS technique: these coatings can have multiple applications (anti-corrosion coatings on metal and ceramic substrates, bio-compatible coatings, etc). A CaO–ZrO₂–SiO₂ glass frit was selected for this attempt. Excellent potentialities emerged (very low porosity), but some problems still existed (big “droplet-like” features on the coating surface), which have recently been largely overcome thanks to process modifications.     

Ethics of family planning

The expression, “ethics of family planning,” it is argued, has no firm meaning, and should not be taken to imply that a full set of moral rules and principles governing family planning has been or is likely to be established. A survey is made of recent views on population and economic and social development, and it is argued that, although there is, indeed, no “universal problem” of population, the optimistic — as well as the pessimistic — view of this relationship is open to doubt. It is further argued that “ethics” cannot be imposed on subject matter of population from without: The very identification of a “problem” of population is evaluative from the start. A scheme of analysis to appraise the ethical status of measures to arrest or promote population growth is proposed, and a number of such measures are critically analyzed.